This invention relates generally to an ink pump control system for controlling ink feed in an ink feeder installed on various types of printing presses, and more specifically to an ink pump control system for controlling ink feed by controlling the revolution of a stepping motor as the drive unit of the ink feeder in accordance with printing speed and printing element ratio (the ratio of printing element area to the sum of a printing element area and a non-printing area on the surface of an object to which ink is fed.)
There exist various types of ink feeders for feeding ink to printing presses for printing newspaper and other printed matter. There is publicly known a typical construction of ink feeder in which an ink pump installed on a printing press is driven by a stepping motor, and ink feed is changed by controlling the revolution of the stepping motor in accordance with each input data of printing speed, printing element ratio and printing density. (Refer to Japanese Published Unexamined Patent Publication No. Hei-1(1989)-174446 and Japanese Published Unexamined Patent Publication No. Hei-1(1989)-174447, for example.)
In the aforementioned publicly known ink pump control system, a frequency division ratio for dividing a basic clock frequency (oscillation frequency) is obtained based on each input data of printing speed, printing element ratio and printing density, and pulses obtained by dividing the basic clock at the frequency division ratio are applied to the stepping motor as the drive unit of the ink pump to effect control so that the optimum ink feed at a given moment can be obtained in accordance with the printing state at that moment.
In the conventional construction where the basic clock frequency is divided at a frequency division ratio obtained by arithmetic operation, and the resulting frequency-divided pulses are applied to a stepping motor, the stepping motor is always kept in a state excited by the frequency-divided pulses of more than zero and less than the basic clock frequency.
This excited state may cause resonance in the stepping motor when rotated at a low revolution, which could in turn produce vibration or shorten the service life of an ink pump driven by the stepping motor.
Furthermore, the coils of the stepping motor are also kept excited even in cases where the ink pump need not be operated as there is no need for ink feeding, or where the printing press is temporarily idled, that is, where printing speed is zero, or where the stepping motor is stopped due to the absence of printing elements on the plate surface to which ink is fed. This may waste electitc power, leading to the reduced life of the stepping motor and increased running cost.